BLACKSSCHEVY

Hey everybody
New to the forum
I have no were else turn
to start i own a 2000 chevy silverado base model came stock with a 4.8 v8 with 350,000 + miles ive owned the truck for 3 years it ran great never gave me a problem until about 6 months ago im cruising and all of the sudden it felt like i was running out of gas and no power like half the power then the engine died so i pulled over and i restarted it hit the gas a few times seemed fine so i drove off a few days later it did it again repeated what i did before and kept driving it so the truck would take 2 or 3 times to start so i changed the fuel pump and fuel filter now it would start fine on first try about a month later it started stumbling again like if i was running out of gas no power this time check engine light came on and i checked it it was p0300 so i went thru a routine tune up spark plugs and wires oil change and a bottle of injector cleaner but p0300 was still there so i started googleing and come to findout there is a long list of things that can cause a p0300 misfire code so knowing that the motor had 350,000 + miles i started looking for a replacement but the 4.8 was still really strong and did not have any noises like lifter taps or knocking great engine other than the misfire so i ended up buying a lq9 6.0 from a 04 escalade along with radiator support with ac condesor and tranny n ps cooler it had 90k miles anyways before I pulled out the 4.8 i wanted to find out what the problem was so I wouldn't have the same problem with the lq9 so I went down the list using parts from the lq9 I swaped maf sensor checked for vac leaks with carb cleaner plugs n wires injectors both coil packs knock crank cam sensors and checked fuel pressure and was 50-60 under a load ( in drive ) and still there it was flashing in my face So I cleared the codes and tryed again and again in my face check engine check engine I let out a scream followed by cursing and punching of air bag so finally I called some one and he did a compression test tested if injectors and coils were firing conclusion was low compression in cylinder #3 it was 90 psi he asured me that was the problem he said any thing under a 100 psi is a problem I told him that the mis would go away and that low compression dosent come and go but I gave up arguing with him about how good the motor ran and started pulling the motor and 2 days later I started the lq9 let it run for a few mins and there it was flashing in my face So I cleared the codes and tryed again and p0300 misfire code again i used the 4.8 harness and computer to start it it ran so I called the guy back we did another compression test and all cylinders on driverside were 180 the passenger side from front to back 150 170 160 125 he said that the 6.0 had the same problem with low compression but i drove the escalade before i pulled the engine and it had plenty of power with no misfire no check engine codes i even drove and did the drive cycle to make sure no check engine light came on
I forgot to mention that I swaped my catalytic converters with some from a 2500 6.0 truck because they are true duel not y pipe like original it passed smog I also wrecked the truck on the driver side minor changed the bed and rear bumper i don't know if that would have anything to do with it
i swaped the computer with one from a 2000 2500 6.0 truck to rule out the computer it dident start my buddy showed me how to do a computer relearn and it started and same p0300 and i got another fuel filter and purged the line to get anything that was in the line out still nothing then i got a test light checked injectors there are pulsating and the coils are giving spark i got loose spark plug and i pluged it to each wire each had spark the only things I haven't changed are 4.8 harness, transmission, throttle body ,02 sensors

i have the 04 lq9 harness dose anybody know if you can plug up to the 2000 fuse block i know that the 04 harness has the electronic gas pedal and oil pressure switch ( 03-06 has 3 wires ) 00-02 has 1 wire ) and ac pump has different plugs i was wondering if i can modify it (repin it ) has any one seen a thread on it
so im stumped going crazy
Please hellllllllp any information or suggestions would be greatly appreciated thanks 👍

Bowtie316

iTrader: (1)

That was really long and I didn't read all of the words.

I would start by checking that all of the sensors are reading correctly with a scanner, ECT, IAT, MAP, TPS, O2, while running and not running.

stage274

My po 300 drove me crazy, but turned out to be a bad battery. Get the battery tested first...